1. Field of the Invention
The present invention relates generally to a system for producing alternating current electric energy. More specifically, the invention describes a hybrid combined cycle power generation facility.
2. Description of the Prior Art
The production of alternating current electric energy is most frequently accomplished by converting thermal energy to mechanical energy that is then used to rotate the magnetic field of an electric generator. Commonly used thermal energy sources include fossil fuel combustion and controlled nuclear reactions. Controlled nuclear reactions and the combustion of fossil fuels are used to produce high pressure, high temperature steam that drives steam turbines. Those steam turbines in turn, convert the energy of the high pressure, high temperature steam to shaft horsepower and in so doing reject, or waste, a great deal of the thermal energy which enters the steam turbine. Conversion efficiencies of modern steam turbines are typically 28-32%. Thus, a large amount of the heat energy generated at the combustion stage is wasted rather than being converted to electric energy. Steam turbine electric generation facilities are relatively expensive to build and consume large amounts of water for cooling purposes. However, one advantage to such steam turbine facilities is that they have the ability to burn low cost solid fuels such as coal or biowaste. Unfortunately, steam turbine facilities that utilize such low cost fuels often produce large amounts of undesirable pollutants and therefore require costly pollution control technology to abate harmful, hazardous or unlawful emissions. In addition such facilities typically require additional permits, over and above the standard permits, for operation.
Fossil fuel combustion within internal combustion engines produces thermal energy in the form of high temperature, high pressure air which is converted to shaft horsepower. Much like steam turbines, internal combustion engines waste most of the thermal energy released by the combustion process. Different internal combustion technologies, e.g., combustion turbines or reciprocating engines, have different thermal energy utilization characteristics, but the conversion efficiencies of internal combustion engines seldom exceed 40%. When compared to steam turbine technology, however, moderncombustion turbine facilities are less expensive to build, use less water, have better conversion efficiencies and are capable of lower pollution emission rates than steam turbine facilities. However, combustion turbines usually require higher cost liquid and gaseous fuels, such as refined oil products or natural gas.
A majority of the thermal energy released during the combustion process in turbines is wasted in the form of hot exhaust gases. It is possible to improve the overall conversion efficiencies of these turbines by capturing a portion of the thermal energy present in the combustion turbine exhaust flow. Heat recovery devices located in the hot exhaust flow can be used to produce steam that is directed to a conventional steam turbine used to generate additional electric energy. The use of combustion turbines with exhaust recovery devices and downstream steam turbines is referred to as xe2x80x9ccombined cyclexe2x80x9d technology. Moderncombined cycle power generation facilities are capable of conversion efficiencies in excess of 50% with some developing technologies nearing the 60% threshold.
There are two basic or fundamental types of combustion turbines available for use in power generation facilities industrial turbines and aeroderivative turbines. Industrial turbines are very robust machines designed to provide highly reliable service in ground based operations driving machinery such as compressors, pumps and electric generators. Industrial turbines tend to be very large and offer good steady-state operating characteristics but exhibit limited tolerance for frequent start/stop cycles, which subject the massive turbine to rapid thermal cycles. Typically, industry design requirements for industrial turbines emphasize high temperature and high load tolerance for extended periods of time with secondary consideration for overall weight. One drawback of industrial turbines is that their large size and heavy weight necessitate in situ disassembly and reassembly which results in extended outages for routine maintenance. Aeroderivative turbines, on the other hand, are often characterized by cutting edge technology to maximize power-to-weight ratios, quick starting times, high fuel efficiency and high start/stop cycle tolerance, all of which are important features since this type of turbine is most often used in aircraft propulsion systems. Materials and components design in aircraft turbines emphasize high strength and low weight with secondary consideration for long term component life. Because they are lightweight and small, aeroderivative turbines are easily removed and repaired offsite when routine repair or refurbishment is required. When removed, the turbine is quickly and easily replaced by a spare turbine thus reducing production outages for routine maintenance. However, one drawback to aeroderivative turbines in relation to industrial turbines is that aircraft turbine technology is more expensive and less robust than industrial turbine technology.
Both industrial and aircraft turbine technologies are used in modern electric energy generating facilities described above. Both technologies can be found in simple cycle, combustion turbine generator facilities and in combined cycle power generation facilities utilizing combustion turbines, exhaust heat recovery and steam turbines. Steam and gas (xe2x80x9cSTAGxe2x80x9d) combined cycle systems are well known in the industry. These systems typically comprise gas turbines, steam turbines, generators and heat recovery steam generators (xe2x80x9cHRSGxe2x80x9d). In any event, these prior art power generation facilities have limited the use of combustion turbines to either industrial turbines or aircraft turbines, but not both.
It would therefore be desirable to have a power generation facility that has the advantages of both an industrial turbine, namely low pollution emissions levels, low capital cost, superior thermal efficiencies, and robust construction, and an aeroderivative turbine, namely rapid response to varied production levels with high thermal efficiencies and quick maintenance turn arounds.
The present invention relates to a system and facility for generating alternating current electric power in which a hybrid, combined cycle power generation facility is provided, including at least one industrial gas turbine, and at least one aeroderivative gas turbine. Such a facility results in lower costs of construction and capital expense and lower costs of production as compared to a combined cycle facility using only aeroderivative turbines. Similarly, the present invention results in a facility that has faster and lower cost start/stop capabilities and better part load fuel efficiencies than combined facilities using only industrial turbines.
In a typical configuration, at least one aeroderivative (xe2x80x9cADxe2x80x9d) turbine is provided. The AD turbine powers a suitable generator and may further provide heated exhaust gas to a heat recovery steam generator, which in turn feeds high pressure, high temperature steam to a steam turbine. The steam turbine also powers a generator. By using an AD turbine, the power system may be brought online quickly to begin producing power. The HSRG recovers heat from the exhaust gas of the turbine and uses the heat to generate steam to power the steam turbine. In this way, the efficiency of the system may be greatly increased.
The system also includes at least one industrial gas (xe2x80x9cIGxe2x80x9d) turbine. The IG turbine typically takes longer to spin up and be brought online, however, once in operation, it is generally capable of higher and more stable output than an AD turbine. As with the AD turbine, the IG turbine has an associated HRSG in thermodynamic communication therewith, to recover heat from the exhaust gas of the turbine to generate steam for a steam generator. The IG turbine also powers a suitable generator.
The HRSG""s, each of which is associated with either an IG or AD turbine, use heated exhaust gas from the turbines to generate steam. This steam is then fed to the steam turbines, which in turn power additional generators. This creates a much more efficient system that using gas turbines alone. Additionally, the HSRG""s may include supplementary firing equipment to produce additional high pressure, high temperature steam and offer additional operational flexibility.
The advantage of the system of the present invention over the prior art systems is that it draws on the benefits of each type of turbine mentioned herein, while diminishing the drawbacks associated with each type of turbine. For example, the AD turbine is able to begin producing power in a relatively short amount of time. Therefore, it can be used to provide power quickly when the system is initially started, while the bigger IG turbine and steam turbine are brought on-line. Both the IG turbine and the steam turbine are capable of producing a greater power output, however, as compared to the AD turbine. Thus, once spun up, the IG turbines and steam turbines can be utilized for a substantial portion of the on-going power production system. The AD turbine may also be used intermittently, for instance, during peak load periods. In this way, the IG and steam turbines may be operated for longer periods of time without the need to vary output. The AD turbine may be used intermittently to provide additional power as necessary. When included in the system design, supplementary firing in the HRSGs provides smooth load transitions while starting and stopping both AD and IG turbines. Supplementary firing also can be used to produce additional high pressure steam for additional steam turbine generator output. Operation with full supplementary firing is reserved for peaking conditions when the resulting decrease in thermal efficiency is secondary to maximum capacity production.